Generation of saw-tooth synchronized voltages



Sept. '29, 1942. e. ZANARINI I 2,297,522

GENERATION OF SAW-TOOTH SYNCHRONIZED VOLTAGES I Filed June'l4, 1940 I 4Sheets-Sheet 1 Fig. 3

18 HHHAIHHH 3% QMXA M Sept. 29,1942. G. ZANARINI 2,297,522 I GENERATIONOF SAW-TOOTH SYNCHRONIZED VOLTAGES Filed June 14, 1940 4 Sheets-Sheet 2Fig. 4

Sept. 29, 1942. GJZAN INI GENERATION 0F sAw-T QTH SYNCHRONIZED YOLTAGESFiled June 14, 1940 '--4 sheets-sheet 3 p 9, 1942- G. ZANARIN. 2,297,522v GENERATION OF SAW-TOOTH SYNCHRONIZED VOLTAGES Filed June 14, 1940 4Sheets-Sheet 4 Patented Sept. 29, 1942 GENERATION OF SAW-TOOTH SYNCHRONIZED VOLTAGES Giuseppe Zanarini, Turin, Italy; vested in the AlienProperty Custodian Application June 14, 1940, Serial No. 340,617 InItaly June 23, 1939 3 Claims.

This invention relates to a system for the generation of saw-toothsynchronized voltages based on the particular features of secondaryemission tubes. This invention has for its object the generation of saidvoltages of adjustable shape and magnitude, the frequency beingcontrolled'by external impulses by means of a single tube of thesecondary emission type and an electronic coupling being employedbetween the secondary cathode and anode of the same tube.

The systems commonly used for obtaining synchronized saw-tooth voltagesemploy two tubes which separately accomplish two different functions.The first tube is used in a pulse generating circuit which may besynchronized by external impulses; the second tube, which is actuated-bythe pulses generated by the first one, is employed in a saw-toothvoltage generating circuit. The magnitude and shape of the signals maybe properly adjusted. According to this invention a simple and efficientsystem has been developed which by uniting the two functions in onesecondary emission tube afiords the generation of saw-tooth voltages ofgreat linearity and of adjustable magnitude.

As is well known, secondary emission tubes, have an active surface(secondary cathode) which, when struck by electronic bombardment, emitsadditional electrons in a larger number named secondary electrons.primary electrons, which are emitted by the primary cathode andcontrolled by the grid, reach through the screen grid the secondarycathode which thus emits further electrons (secondary electrons) in alarger number, that are then attracted by the plate to which a propervoltage is applied. Consequently, the current fiowing through thesecondary cathode has a negative direction and the secondarycathode-primary cathode path may be considered as a negative resistance.Moreover, it is known that by placing a positive resistance in parallelwith a negative resistance a current will be set up, the value of suchcurrent being steady or unsteady; more particularly, the current isunsteady where the positive resistance has an actual value higher thanthat of the negative resistance. In this case, theoretically, anindefinite increase in current and voltage at the terminals of the setof resistances in parallel will take place. In practice, such increasein current will reach the limits afforded by the shape of the negativeresistance characteristic curve, which is never perfectly linear and ofindefinite length. In the The bombarding or case of a secondary emissiontube, as said above, 55

the negative resistanceis represented by the secondary cathode-primarycathode path and its value may vary from a'minimum, determined by thetube characteristic, to a maximum coinciding with the infinite value asa function of the potential difference existing between the control gridand the primary cathode; the minimum value of the negative resistancecorresponds to the zero value of said potential difference, while themaximum value will obviously correspond to cut-off. Therefore, byplacing between primary cathode and secondary cathode an ohmicresistance having an actual value higher thanthe minimum value of thesecondary cathode negative resistance, it is possible to go over from asteady to an unsteady condition, or vice versa, by simply adjusting inthe proper waythe control grid voltage. When set for stability, thevoltage appearing on the secondary-cathode will be the product of thecurrent by the positive resistance. When set for instability, saidvoltage will increase, the velocity depending upon the time constant ofthe circuit, until it reaches the maximum limit of the current suppliedby the cathode under these particular conditions of operation. It isclear that this instability is not due to the coupling between thesecondary cathode and control grid. By introducing this coupling, forinstance by means of a capacity, the instability phenomenon isemphasizedsince, owing to this coupling, the value of the negative resistanceofthe secondary cathode-primary cathode path is actually decreased.

In this case it follows that, owing to the decreased value of thenegative resistance during the dynamic condition, the instabilityphenomenon may also be obtained with positive parallel resistances of arelatively small value, in any case smaller than that of the negativeresistance in a static condition which would not take place unless saidcoupling is resorted to. The invention is based on this condition inorder to accomplish the first operation, that is, the generation ofsynchronized impulses. Current impulses may also be generated by virtueof either capacity or inductive coupling between the secondarycathodeand the control-grid while thesynchronizing signals may be appliedthrough a capacity either to the secondary-cathode or the control grid.

Current impulses may also be generated by virtue of either capacity orinductive coupling between the secondary cathode and screen grid; inthis way, the control grid remains free and 2 may be used forsynchronization by means of external signals.

Therefore, the grid impedance of the secondary emission tube is notbound to the characteristics of the impulse generating circuit and maybe of any value. Moreover, through the strong controlling action of thecontrol grid on the emission of the tube, synchronization may beeffected with synchronizing signals having considerably small voltageand current parameters.

Synchronization may also be effected by operating on either thesecondary cathode or the screen grid.

Consequently, the circuit lends itself to a double synchronization,firstly, a synchronization which I call main synchronization may be madethrough the control grid and, secondly, a synchronization which I calldriven synchronization, may be made through either the secondary cathodeor the screen grid. If the two synchronizing signals are of a differentfrequency, the impulses may be generated by the secondary cathode onsuperposition of both actions of the synchronizing signals.

Finally, in the case of regeneration between the secondary cathode andscreen grid the coupling may be obtained through direct connection.

The accompanying drawings show, by way of example only, some embodimentsof the invention.

Figure 1 shows the diagram of a self-excited impulse generatorsynchronized by external positive impulses;

Figure 2 is a diagram showing the shape of the voltage on the secondarycathode of the synchronized impulse generator, of which Figure 1 showsthe diagram.

Figure 3 shows a diagram of a blocked impulse generator operating underthe action of synchronizing impulses only being a modification of thecircuits included within the dash-line rectangle of Fig. 1 and may besubstituted for the circuits included within said rectangle.

Figure 4-. shows the diagram of a saw-tooth impulse generator by meansof a condenser discharge.

Figure 5 shows a method of adjusting the tooth shape.

Figure 6 shows the diagram of a double-synchronization impulse generatorwith a capacitative coupling between the secondary cathode and screengrid.

Figure 7 shows a further modification, in which the reactive coupling isobtained through direct connection.

Referring to Fig. 1 which considers only the first operation, that is,the generation of synchronized impulses having certain characteristics,no use is made of the anode tube.

The tube adopted for this purpose may be a Philips 4696 type or anyother tube having similar characteristics in which 2 is the secondarycathode, -3 the screen grid, 4 the control grid, 5 the cathode and 6 theanode. l are the anodic supply terminals.

In this case, the control grid 4 is not biased, but is directlyconnected to ground and, therefore, to the primary cathode throughresistors l and I I, the purpose of which will be explained hereinafter.Consequently, according to what we have detailed above, the negativeresistance of the secondary cathode-primary cathode path reaches itsmaximum value. The resistor I connected between the secondary cathodeand high voltage supply supplies to the secondary cathode an initialpositive voltage, so that at the start the primary electrons can reachthe cathode. Its value is such that the cathode is biased with 30 or 40volts. The screen grid voltage is taken from the voltage divider l2, l4:the voltage is free from any variable component owing to the filteringaction of the condenser It.

A resistor 8 is connected between the secondary cathode and primarycathode and its value is such that the set of resistors 8 and itconsidered in parallel have an actual value higher than that of theprimary cathode-secondary cathode path. In accordance with thestatements made above, the circuit is in an unsteady condition and as aconsequence, the secondary cathode voltage increases independently perse. At this point it should be noted that, on account of the capacitivecoupling existing between the secondary cathode and control grid, theinstability phenomenon might arise even for values considerably smallerthan that of the resistor 8.

The design of the circuit could therefore be Lased on this circumstance,that is on the actual Value taken by the negative resistance in adynamic condition".

However, the operation of the circuit is the same and the instability iscaused by an excess positive resistance as compared with the amount ofnegative resistance, considering the phenomenon in either a static ofdynamic condition. In this example, however, for the sake of simplicity,I consider the first case only. The condenser 9 is connected to thesecondary cathode and is in series with resistor H] which is connectedto the control grid; its charge increases by effect of the grid currentof the tube and the current flowing through resistor l I. The grid thentakes a slight positive potential, that lasts all the time during whichthe secondary cathode voltage increases. As soon as this increaseceases, owing to characteristic limitation, the positive grid voltagebegins to decrease effecting a further charge of condenser 9.

The result is a decrease in the secondary current and correspondingvoltage. At a certain point the grid current ceases and the condenser 9then tends to maintain its charge owing to the relatively high value ofresistor ll. Consequently, the control grid voltage becomes negativecausing a further decrease in the secondary cathode voltage. It is clearthat the phenomenon goes through a second phase, reverses to the firstone with increasing velocity, until the secondary cathode has reachedthe bias voltage supplied by the voltage divider '8, I5. Under suchcondition, however, owing to the large charge of condenser 9, the tubeis blocked and the condition lasts until the condenser has dischargeditself (through resistor H) to such an extent as to restore the unsteadycondition. Thereupon another cycle, equal to the one just described,takes place. The generation of a series of impulses is thus obtained,said impulses being of a relatively small duration, separated by shortintervals of time which depend upon the time constant of the network 9,l I and theanode supply condition.

The duration of each impulse depends instead upon the time constant 9,10 since resistor ll] affects the time needed for charging up condenser9 during the unsteady phase. The voltage impulse on the secondarycathode is positive and its shape is of the type shown in Fig. 2. Thevoltages V are plotted on the ordinates and the times t on theabscissae. The voltage 30 designates the impulse magnitude and its valueis determined by the tube characteristic and operating conditions. Time32 depends upon the value of capacity 9 and resistor l and the largerthese values the greater the time will be.

The slope of the ascending and descending portions depends greatly uponthe value of resistor 8 and the tube internal capacity. By suitablyadjusting the elements of the circuit it is possible to vary all thecharacteristics of the impulse.

The impulse generator just described is self-. excited and may besynchronized by external positive impulses fed on the secondary cathode.For certain uses, however, it is preferable for the generator to benormally blocked and operate only under the action of the synchronizingimpulses. As shown in Fig. 3 which shows a modification of the circuitsincluded in the dash-line rectangle in Fig. 1, this is obtained bysimply supplying to the control grid a negative bias voltage l8 such asto keep the tube in a steady condition. A positive impulse of sufilcientmagnitude applied through the terminals l'! and a coupling condenser 16to the secondary cathode reaches the control grid through condenser 9causing an unsteady condition and therefore generating an impulse in themanner explained above. The second operation which is the generation ofsawtooth synchronized voltages, is effected by employing the plate ofthe tube which remained out of use when performing the first operation.In fact, during generation of the impulse, the anode resistance of thetube, starting from an infinite value corresponding to cut-off reaches aminimum value, corresponding to the maximum magnitude of the impulse anddepending upon the characteristics of the tube and supply operatingconditions, resuming the infinite value when the impulse ceases. Thisvariation in resistance is employed according to the invention for thegeneration of the saw-tooth voltage by means of the discharge of acondenser. In Fig. 4, a practical arrangement of this system is shown.At each impulse capacity 23 is partially discharged and charges up againduring the intervals between the various impulses with a velocitydepending upon the value of resistor 22 or by varying the Value ofcapacity 23 and the larger the Value of these elements the smaller themagnitude will be. In order to obtain an efficient discharge ofcondenser 23, its capacity should not exceed certain limits, whichdepend upon the value of the anode resistance of the tube. In theexample of Fig, 4, in which the capacity is assumed to be of a fixedvalue, the magnitude adjustment is obtained by means of resistor 22 andthe variation in the saw-tooth slope, that is (referring to Fig. thesetting of time 33 and 34, is obtained by adjusting the duration of theimpulse according to the circumstances previously set forth; the time 35being substantially equal to the duration of the impulse producing thedischarge of condenser 23.

In the circuit diagram given in Fig. 4, it is possible to go over froman almost steady condition (blocked impulse generator) to an unsteadycondition (self-excited generator) by simply adusting the bias voltageof the tube by varying resistor 22. The capacity 20 should be of a lowreactance for the frequencies concerned and always much lower than thevalue of resistor I9. The condenser 24 (the reactance of which should bemuch lower than the value of resistor 8) permits by varying the tap 26the adjustment of the regeneration effect and the slope of the ascendingand descending portions of the impulses.

The saw-tooth synchronized voltage generator just described isparticularly suited for the synchronization in television receivers orthe actuation of the time axis in cathode ray Oscilloscopes and thelike.

In Fig. 6 the reactive coupling is again between the secondary cathodeand screen grid through capacity 35, but there is a doublesynchronization, namely a main synchronization applied to terminals 3'!and a driven synchronization applied to terminals [1.

The considerations set forth above also apply to this embodiment asregards the degree of regeneration, instability condition, generation ofthe saw-tooth voltage operated by the anode circuit, etc.

In Fig. 7 the reactive coupling between the screen grid and secondarycathode is obtained by means of direct connection.

What I claim is:

1. In a saw-tooth synchronized wave generator, in combination asecondary emission highvacuum thermionic tube including a primarycathode, a control grid, a screen grid, a secondary cathode emittingsecondary electrons, and an anode, in the order named, means forconveying the electrons emitted by the primary cathode through thecontrol grid and screen grid and means for conveying the secondaryelectrons to the anode; a reactive circuit generating impulse waves of aconstant magnitude and considerable energy, in which the reactive effectis obtained by utilizing the negative resistance offered under certainfeed conditions by the secondary cathodeprimary cathode path in saidsecondary emission tube, said circuit being connected to the electrodesof the secondary emission tube comprised between the primary cathode andthe secondary cathode both included; means for synchronizing saidimpulses by external impulses containing less energy and actuating saidelectrodes; a saw-tooth generating circuit formed by the internal anoderesistance of the secondary emission tube, its value being controlled bythe impulses generated by the reactive circuit through theelectroniccoupling existing between the secondary cathode and the anodeof said tube and by a capacity connected between the anode and primarycathode in said tube, said capacity being periodically charged by thecurrent flowing through a resistance connected to said capacity and to asource of direct voltage, and discharged by said internal anoderesistance of the secondary emission tube, the discharge effectprevailing during said synchronized impulses and the charge effectprevailing during the time intervals between two successive impulses.

2. In a saw-tooth synchronized wave generator, in combination asecondary emission highvacuum thermionic tube including a primarycathode, a control grid, a screen grid, a secondary cathode emittingsecondary electrons, and an anode, in the order named, means forconveying the electrons emitted by the primary cathode to the secondarycathode through the control grid and screen grid and means for conveyingthe secondary electrons to the anode; a direct current anode supplysource, means for applying to the screen grid and the secondary cathodein said secondary emission tube two positive biasing voltages withrespect to the primary cathode, the values of said voltages being lowerthan the total voltage supplied by said current source, means forapplying a positive biasing voltage to the primary cathode with respectto the bias voltage existing on the control grid of said tube; a circuitgenerating impulse waves of considerable energy, including a resistorhaving one terminal connected to the control grid of said tube and theother terminal connected to an impedance connected to the negativeterminal of the direct current source, means for coupling in phase thesecondary cathode to the junction point comprised between said resistorand said impedance in order to reduce the negative differentialresistance ofiered by the primary cathode-secondary cathode path undercertain feed conditions in the secondary emission tube, an impedanceconnected between the primary cathode and secondary cathode, the ohmicvalue of said impedance being larger for the operating frequencies thanthe minimum value of said negative differential resistance, said circuitgenerating impulses owing to the instability phenomena which happenwhenever the instantaneous value of the control grid negative voltagewith respect to the primary cathode is lower than a certain limit value,this value depending upon the characteristics of the tube and the valueof said impedances; means for applying to said impulse wave generatingcircuit positive synchronizing impulses of lower energy, which,affecting said instantaneous grid voltage may produce, if of sufficientmagnitude, said instability conditions which cause the circuit togenerate an impulse the duration of which, in a certain degree, de-

pends upon the value of said resistor connected to the control grid ofsaid secondary emission tube, the magnitude of said impulse dependingupon the characteristics of said tube, the supply voltages and thecharacteristics of the anode circuit of said tube; a saw-tooth wavegenerating circuit including a capacitor connected between the anode ofsaid secondary emission tube and negative terminal of the direct currentsource and a resistor connected between said anode and the positiveterminal of said source, said condenser being discharged at each impulsegenerated by the impulse wave generator by the anode current of thesecondary emission tube, the value of said current being controlled bysaid impulse generator through the electronic coupling existing betweenthe secondary cathode and anode inside said tube, said condenser beinginstead charged by the current flowing in the resistor connected to saidanode during the time intervals which happen between two successiveimpulses, setting up at the terminals of said condenser a voltagevariable with time according to a saw-tooth shape, said voltage being insynchronism with the external impulses applied to the impulse generatingcircuit and its magnitude depending greatly upon the values of saidcapacitor and resistors.

3. In a saw-tooth synchronized wave generator, in combination asecondary emission highvacuum thermionic tube including a primarycathode, a control grid, a screen grid, a secondary cathode emittingsecondary electrons, and an anode, in the order named, means forconveying the electrons emitted by the primary cathode to the secondarycathode through the control grid and screen grid and means for conveyingthe secondary electrons to the anode; a direct current anode supplysource, means for applying to the secondary cathode in said secondaryemission tube two positive biasing voltages with respect to the primarycathode, the values of said voltages being lower than the total voltagesupplied by said current source, means for applying a positive biasingvoltage to the primary cathode with respect to the bias voltage existingon the control grid of said tube; a circuit generating impulses ofconsiderable energy, including a resistor connected between thesecondary emission tube control grid and the negative terminal of thedirect current source, a resistor one terminal of which is connected tothe screen grid of said secondary emission tube, while the otherterminal is connected to an impedance connected to the positive terminalof the direct current source, means for coupling in phase the secondarycathode to the junction point comprised between said resistor and saidimpedance in order to reduce the negative differential resistanceoffered by the primary cathode-secondary cathode path under certain feedconditions in the secondary emission tube, an impedance connectedbetween the primary cathode and secondary cathode, the ohmic value ofsaid impedance being larger for the operating frequencies than theminimum value of said negative differential resistance, said circuitgenerating impulses owing to the instability phenomena which happenwhenever the instantaneous value of the control grid negative voltagewith respect to the primary cathode is lower than a certain limit value,this value depending upon the characteristics of the tube and the valueof said impedances; means for applying to said impulse wave generatingcircuit positive synchronizing impulses of lower energy, which,affecting said instantaneous grid voltage may produce, if of sufficientmagnitude, said instability conditions which cause the circuit togenerate an impulse the duration of which partly depends upon the valueof said resistor connected to the screen grid of said secondary emissiontube, the magnitude of said impulse depending upon the characteristicsof said tube, the supply voltages and the characteristics of the anodecircuit of said tubes; a saw-tooth wave generating circuit including acapacitor connected between the anode of said secondary emission tubeand negative terminal of the direct current source and a resistorconnected between said anode and the positive terminal of said source,said condenser being discharged at each impulse generated by the impulsewave generator by the anode current of the secondary emission tube, thevalue of said current being controlled by said impulse generator throughthe electronic coupling existing between the secondary cathode and anodeinside said tube, said condenser being instead charged by the currentflowing in the resistor connected to said anode during the timeintervals which happen between two successive impulses, setting up atthe terminals of said condenser a voltage variable with time accordingto a saw-tooth shape, said voltage being in synchronism with theexternal impulses applied to the impulse generating circuit and itsmagnitude depending greatly upon the values of said capacitor andresistors.

GIUSEPPE ZANARINI.

